How to make chatbot using NLP like Dialogflow?
You are right that you will have to implement the above steps before building any chat bot, this is because your computer doesn't understand text like you and I do. Therefore, text has to be pre-processed(converted) into a format that the computer can work with Tokenization, Parts of Speech Tagging and Named Entity Recognition are such pre-processing techniques.

Rule based means when you create rules for deciding how should your chat bot behave in a given situation.

You can have a look at this blog which teaches how to deploy a chat bot using DialogFlow on Slack - https://www.analyticsvidhya.com/blog/2018/03/how-to-build-an-intelligent-chatbot-for-slack-using-dialogflow-api/